James Schoffstall of Liberty University and Stuart McGill of the University of Waterloo offer tips for training core muscles.

Good results can come from unexpected places, including the weight room. James Schoffstall, director of exercise science at Liberty University in Virginia, says dead lifts and squats are proven ways to strengthen the core. As he explains, the core muscles have to stiffen throughout the lifts. He adds that the moves prepare the body for real-life activities outside of the gym. "Picking up a suitcase — that's a dead lift," he says. "Getting up off the toilet — that's a squat."

It doesn't take huge amounts of weight to get results, Schoffstall says. He recommends trying a simple "suitcase squat." Stand up straight holding a 5- or 10-pound dumbbell at your side in one hand. Then extend your opposite arm and slowly squat down as if you were about to sit in a chair. Repeat 10 times or so and then switch sides.

Over the years, Stuart McGill, the director of the spine biomechanics laboratory at the University of Waterloo in Canada, has settled on his own "big three" core exercises that he recommends as part of a comprehensive workout routine. The exercises — known as the curl up, the side bridge and the bird dog — were designed to provide the most core benefit without putting undue stress on the spine.

"A lot of science went into developing these exercises," he says. He adds that many serious athletes will need more intense core workouts that go beyond the basic three.

McGill and an assistant demonstrate these exercises in a YouTube video called "Train the Core the Right Way." Here are the routines, briefly. In each, you should hold the position for up to eight seconds at a time. You can gradually increase the number of repetitions as your core gets stronger.

Curl up: Lie on your back with one knee bent and one leg straight on the floor. With your hands under the small of your back for extra support, barely lift your head and shoulders off the ground.

Side bridge: Lie on your side. Using your forearm as a brace, lift your body up so that only your arm and the side of your foot are touching the ground. (Beginners may want to support themselves with their knees.) Your body should be completely straight.

Bird dog: Start on all fours with your hands directly under your shoulders and your knees directly under your hips. Point one arm straight forward and stick the opposite leg straight out, once again keeping the spine still and straight.